jumped timing?
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jumped timing?
I hope someone out there can help me! When I have the #1 cyl on top, should the marks on the balancer line up with the pointer at 8:00? When I put my timing light on it the marks are at about 12:00? It cranks up fine but when I idle in drive with the brakes on it wants to die out? The rotor seems to be pointing at the #1 wire post when #1 is up.
Last edited by bremon140; Nov 13, 2005 at 01:43 PM.
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From: PacNW
I'm not sure what your questions is. 8:00? 12:00? Do you mean 8 degrees and 12 degrees or 8:00 and 12:00 as in where the numbers are on a clock?
TDC is a mechanical relationship between the crankshaft, rods, pistons & the harmonic balancer. It's not adjustable. Whether or not the valves are closed at that point is a relationship between the crank, cam, timing chain, & valvetrain. It's also not adjustable unless you're changing the camshaft & timing set.
When you set the timing you're telling the engine where in relationship to TDC to fire the spark plug. Obviously that is adjustable. When you set the timing you need to make sure the vacuum hose is pulled off the vac adv module on the distributor and plugged. The idle mixture & speed also need to be set to specs for your vehicle. You adjust the timing by turning the distributor until you get the desired amount of advance BTDC and then readjust the idle speed as necessary.
TDC is a mechanical relationship between the crankshaft, rods, pistons & the harmonic balancer. It's not adjustable. Whether or not the valves are closed at that point is a relationship between the crank, cam, timing chain, & valvetrain. It's also not adjustable unless you're changing the camshaft & timing set.
When you set the timing you're telling the engine where in relationship to TDC to fire the spark plug. Obviously that is adjustable. When you set the timing you need to make sure the vacuum hose is pulled off the vac adv module on the distributor and plugged. The idle mixture & speed also need to be set to specs for your vehicle. You adjust the timing by turning the distributor until you get the desired amount of advance BTDC and then readjust the idle speed as necessary.
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Thanks for the reply. I'm familiar with the nuances of spark distribution, my situation is that my factory timing marks on the balancer line up with the pointer (mounted on the engine block at the 8-o'clock position) when the #1 cyl is at the BOTTOM of the stroke. When I bumped it around to the TOP of the stroke and marked the bare metal on the balancer with white-out, it is exactly 180* opposite of the factory timing marks. Cranks & runs great, just can't tweak it with the timing light and a paint line...CM
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From: PacNW
I'm a little confused as to how you read the mark if the timing indicator is on the bottom of the engine. The timing pointer should be at approx 10:00. There is a 2nd probe receptacle below the pointer which is used with an electronic timing device.
Last edited by Bill_Beyer; Nov 17, 2005 at 07:04 PM.
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Yes the factory marks are engraved in the balancer. My "pointer" is rounded on the end with a hole in it. It is located at the 8-o'clock position, not on the bottom(6-o'clock), looking front to rear. looks like its been there since day one. I was told it's a 400,don't know. It does have a 4in stroke. With #1 cyl on top, the engraved marks are at the 2-o'clock position , barely visible behind the rad hose, A/C comp.,pulleys and belts
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From: PacNW
Ah, that explains a lot. First, you're looking at the probe receptacle not the timing pointer. That will never line up with the balancer markings. Second, you have A/C so try looking for the timing pointer from the left side of the engine instead of the right. It should be about 2:00. If it's not there then it's probably been removed or broken off.
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From: chicago burbs
other possibles are that the outer ring on the balancer has spun, or the balancer has been replaced with one that has timing marks for a pointer in a different spot. i have this situation on my engine right now, what i did was put a timing tape on the balancer after i accurately located TDC.
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Not really...As I stand in FRONT of the engine, it seems impossible for the pointer to be at the 2:00 position. It is so far under the lower rad. hose, water pump and A/C comp. that I can't even see it from the bottom, much less even get a strobe on it. The pointer on my '78 400 supercab is located at about the 10:00 position, in plain view under the alt...It also seems unlikley that the outer ring spun exactly 180*! Possibly an alien balancer?
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From: PacNW
Well I went back and double checked my FoMoCo shop manual and it specifically states that on the 351M/400 with A/C the timing pointer should be viewed from the left side of the engine (right when you're standing in front of it). Also logic would dictate that if you get the #1 cylinder to TDC and the marks on the balancer are at 2:00 there oughta be a pointer in the general vicinity.
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